The time evolution of dielectric barrier discharge driven by nanosecond pulse high-voltage power is investigated by high-speed video analysis, electrical measurements and spectral diagnostics. It is found that the discharge mode generally goes through the evolution process of filamentary discharge → diffuse discharge → filamentary discharge with the increase in discharge cycle. The time-dependent changes in the standard deviation of image gray levels indicate that the discharge uniformity first improves and then deteriorates in this evolution process. The different pre-ionization density and modulated distribution of space charges and surface charges are considered to be the main reasons for the time evolution of discharge uniformity. In addition, the experiments under different frequencies and voltages show that the transition of the discharge mode is more likely to occur at higher frequency and higher voltage. Further measurement and calculation reveal that the discharge at high frequency and high voltage has the same characteristics, that is, high pre-ionization degree, thick filament diameter and short time lag. These characteristics usually lead to higher seed electron density, larger critical avalanche size and weaker lateral inhibition effect, which make the discharge mode transition more likely to occur.

A magnetic field, with the direction parallel to the electric field, is applied to the repetitively unipolar positive nanosecond pulsed dielectric barrier discharge. The effect of the parallel magnetic field on the plasma generated between two parallel-plate electrodes in quiescent air is experimentally studied under different pulse repetition frequencies (PRFs). It is indicated that only the current pulse in the rising front of the voltage pulse occurs, and the value of the current is increased by the parallel magnetic field under different PRFs. The discharge uniformity is improved with the decrease in PRF, and this phenomenon is also observed in the discharge with the parallel magnetic field. By using the line-ratio technique of optical emission spectra, it is found that the average electron density and electron temperature under the considered PRFs are both increased when the parallel magnetic field is applied. The incremental degree of average electron density is basically the same under the considered PRFs, while the incremental degree of electron temperature under the higher-PRFs is larger than that under the lower-PRFs. All the above phenomena are explained by the effect of parallel magnetic field on diffusion and dissipation of electrons.

The effect of flowing air on dielectric barrier discharge excited by alternating voltage was investigated by high-speed video analysis and electrical measurements. The discharge was still in filamentary mode in flowing air, and the space-time distribution of filaments was changed by airflow. With the increase in airflow velocity, the space-time distribution of discharge filaments shown in top view images went through four phases, that is, spot-like distribution, line-like distribution, cotton-like distribution, and stripe-like distribution. Accordingly, the motion and morphology of discharge filaments shown in side view images also presented four phases: remaining still and straight between adjacent cycles, moving and bending downstream, almost remaining still and straight between adjacent cycles, and moving and bending downstream again. Different motions of filaments were considered to be the reason for the changed distribution of filaments in flowing air. In addition, the intensity of discharge in flowing air was enhanced by increasing the gas gap and discharge frequency. At high discharge current, larger airflow velocity was needed to reach phase transition. The changed distribution of micro-discharge remnants in flowing air can be responsible for the phase transition. Micro-discharge remnants redistributed during the time interval of adjacent half-cycle discharges, under the action of various forces, such as electric field force, drag force, repulsive force, electrostatic coupling force, and trap binding force. The changed position of micro-discharge remnants led to the complex motions of discharge filaments and further resulted in the changed space-time distribution of filaments.

The plane-to-plane dielectric barrier discharge within 5 mm air gap driven by repetitive nanosecond pulses is studied. A water resistance (WR) is connected in parallel with the discharge circuit. For the discharge without the WR, two reverse discharges occur in the falling front of the voltage pulse, and besides, the primary discharge occurs in the rising front. For the discharge with the WR, only the primary discharge takes place, and the voltage waveform is changed into the unipolar positive voltage pulse with the elevated fall time. Additionally, the discharge with the WR displays the intermediate between the traditional diffuse and filamentary modes. Moreover, the uniformity of the discharge with the WR is increased as the pulse repetition frequency decreases from 1200 Hz to 100 Hz. The above observations in the discharge with the WR are mainly attributed to the increase in the residual charge at the inception of the following pulsed discharge.

Dielectric barrier discharge (DBD) with better uniformity, excited by nanosecond pulses, is achieved within 8 mm air gap by using a self-designed DBD structure in airflow. The self-designed DBD structure is characterized by adding a metal rod (MR) in discharge gap, which will produce a local strong electric field and induce surface and volume discharge. It is observed from sequential single periodic discharge images that the uniformity of discharge starts from the electrode edge at the airflow inlet and moves gradually toward downstream under the action of airflow. When the uniformity of discharge is transmitted to a nearby of MR, a stable uniform and symmetrical annular discharge configuration is formed. Besides, that uniform area can be expanded by adding many MRs or MR array in the discharge gap. There is an optimum distance between every two MRs to produce a continuous and maximum discharge area with better uniformity. The above phenomena are mainly ascribed to the change of electric field distribution caused by MR and the charged particles redistribution induced by airflow.